The present invention also relates to soles provided with such vapor-permeable element and to shoes comprising such soles.
Shoes with soles that are impermeable to water and vapor-permeable (permeable to water vapor) and are made of plastic material have now been known for several years.
Their purpose is to allow the escape of the water vapor generated by the foot by sweating; as is known, this sweating is greater at the interface between the foot and the sole.
An important example of this type of sole is disclosed in Italian patent no. 1282196.
The sole disclosed in this patent is structured with a mid-sole provided with a membrane made of a material which is impermeable to water and permeable to water vapor and is associated with a lower protective layer of a material which is resistant to hydrolysis, water-repellent, vapor-permeable and/or perforated, and a tread made of perforated elastomer is joined hermetically to the mid-sole along its perimeter.
Italian patent no. 1293474 discloses a technical evolution of the above described sole.
This patent discloses a sole produced with a particular production method which has allowed to reduce costs and increase manufacturing precision.
Such sole is constituted by a tread which is overmolded on a mold insert constituted by a portion made of perforated plastic material, above which a felt and a membrane made of a material which is impermeable to water and permeable to water vapor are rigidly fixed.
Such membrane is joined hermetically along its perimeter to the portion made of perforated plastic material, which in practice acts as a mid-sole portion and has supporting functions (in cooperation with the tread) for the foot in the region that corresponds to the position of the membrane (the vapor permeation region).
Generally, the insert has such dimensions as to occupy the front portion of the sole, the one that corresponds to the region where the foot sweats the most.
The overmolded tread has a plurality of holes at such insert.
The region for evacuation of the water vapor, however, is limited by the number and areas of the holes of the tread and of the insert; to increase this evacuation area, it would be necessary to increase the number of holes, keeping their diameter small, in order to avoid the penetration of pointed objects which might ruin the membrane by piercing the felt.
One solution is shown for example in WO 2004/028284 by the same Applicant.
This solution uses a sole in which there is a supporting layer, which is provided with a large portion which is diffusely perforated or otherwise vapor-permeable (having, for example, dimensions which are substantially comparable to the length of the sole); the felt and the membrane made of a material that is impermeable to water and permeable to water vapor is positioned above such large portion. Such supporting layer is formed for example by the assembly insole of the shoe on which the sole is to be provided.
A mid-sole with supporting functions is molded perimetrically with respect to the large portion of the supporting layer (the assembly insole), and the tread in turn is overmolded perimetrically thereon; the tread can include studs for contact with the ground which are overmolded directly on the supporting layer.
However, this solution is not ideal in terms of flexibility in the production of shoes with vapor-permeable and waterproof soles that are structured very differently from each other (depending on the technical requirements).
Another solution to the problem of increasing the evacuation of water vapor from a sports and competition shoe is the one disclosed in U.S. Pat. No. 6,817,112 by Adidas International B.V.
This document discloses a sole which is composed of a supporting layer, which is substantially as long as the entire sole and has a plurality of diffusely perforated regions.
A diffusely perforated inner sole is arranged above the supporting layer.
The layer supports two distinct portions of shock absorbing mid-sole, respectively a front portion and a rear portion.
A function of the supporting layer is to allow the various parts of the sole to stay together, constituting the structural connection of the assembly.
The central portion of the supporting layer is not associated with the mid-sole and has some of the diffusely perforated regions connected directly to the outside of the sole.
Other regions of the diffusely perforated regions can be located at the front and rear of the supporting layer; in this case, the mid-soles have large holes (this expression being used to designate a hole on the order of at least one square centimeter) at such regions, so as to allow their connection to the outside of the shoe.
A tread is associated below the mid-soles.
The mid-soles have a certain height in order to ensure the correct distance of the diffusely perforated regions from the ground; such regions in fact must not touch the ground and in practice correspond to ventilation openings for the shoe, which must not be obstructed in order to be able to perform their function.
Moreover, such diffusely perforated regions must be raised from the ground enough to prevent any inflow of liquids into the shoe.
However, this type of sole is extremely particular, since it can be used only for a type of shoe that is particularly raised from the ground and cannot be used in rainy seasons, due to the risk of internal penetration of liquids.
However, the use of a Gore-Tex® membrane, associated with such diffusely perforated regions, is provided as an option.
Actually, in the type of shoe disclosed in the patent cited above it is not possible to use the membrane conveniently, since such membrane is extremely delicate; in order to try to limit any breakage, it is arranged at a considerable distance from the ground, so as to avoid contact with pointed and hard objects.
Moreover, it should be noted that the content of the cited patent is silent about how the membrane is positioned and how to provide a seal in order to prevent the rise of liquids laterally with respect to the membrane, these features being fundamental in order to ensure waterprooffess.